The pride and passion of a manhunter

Crusading UN war crimes prosecutor Carla Del Ponte is about to end an eight-year mission that has convicted 53 killers. In this exclusive interview with Ed Vulliamy in The Hague, she looks back at her triumphs and failures

She is compact, with a shock of white hair and darting eyes that give more than a hint of the passions within the wrapping of the practice of law and its dry lexicon.

Carla Del Ponte, the world's most powerful criminal lawyer, has been chief prosecutor of the international criminal tribunals for the former Yugoslavia and Rwanda for eight epic years. A week tomorrow she gives her last report to the United Nations Security Council and leaves The Hague on New Year's Eve.

In her first valedictory interview, she told The Observer of the bittersweetness of the tribunal's successes and failures to conclude: 'For me, it started with the victims, continued for the victims and it ends with them. That is what I have to tell myself - if we have established the record of what happened to the victims, then we have achieved something'.

Del Ponte is hardly a modest or retiring woman, but on her desk, by way of salt in her own wound, lies an adulatory pennant showing the Bosnian Serb general Ratko Mladic, with its sadistic squint. This is the man - along with political counterpart Radovan Karadzic, the Bosnian Serb leader - whose continued freedom, 12 years after they were indicted for genocide, is a thorn in Del Ponte's side. Alongside that of the late Serbian President Slobodan Milosevic, their pictures hang on her office walls and taunt her. 'To one side, I can look at everything this tribunal has done, to establish that these crimes were committed and give voice to the victims. Then I look the other way and have Karadzic and Mladic, wanted for ordering those very crimes and for genocide at Srebrenica, still at large after 12 years of indictment and my eight years here. Then I feel terrible disappointment'.

There are those who see the delivery of Karadzic and Mladic to The Hague as the litmus test of the tribunal's cogency, especially as its biggest catch - Milosevic, who unleashed the killing - cheated justice by dying on trial. But this is churlish. The tribunal - the first of its kind since Nuremberg - has convicted 53 people, both masterminds and lowly perpetrators of horrendous crimes committed during the violence that broke up Yugoslavia. The man who ran the Srebrenica massacre, General Radislav Krstic, was convicted of genocide, reduced on appeal to aiding and abetting genocide. The Srebrenica case was an end piece to years of other criminal violence in Bosnia, much of it preventable by an international community which established the tribunal as an act of contrition.

In successfully prosecuting Momcilo Krajisnik, co-President with Karadzic, Del Ponte's office jailed the eminence grise of the pogrom. Another of Karadzic's co-Presidents, Biljana Plavsic, entered a rare plea of guilty to crimes against humanity. Another conviction was of Milomir Stakic, who oversaw the gulags in north-west Bosnia - for which he was sentenced to life, reduced on appeal to 40 years. Convictions of Bosnian Serbs from the town of Foca established rape as a war crime, and the case of Stanislav Galic established the 'legal' siege of Sarajevo as a war crime. The leadership of a 'sideshow' war against Bosnia's Muslims mounted by the Croats is on trial, as is the Bosnian Muslim army general Rasim Delic.

'A crime is a crime, whether in the smallest village or at Srebrenica. I will not have a category one, two, or category three defendant. To their victims, they are the same thing and I do this for the victims,' says Del Ponte. She is fiercely critical of how victims are cross-examined. She describes hearing a rape victim questioned in a way 'to invalidate her testimony, suggesting it could not have happened because she was not able to wash herself, and that the next soldier would not then rape her. I cannot imagine what she must have been feeling, and we oppose that kind of questioning.'

Born in Lugano on Switzerland's border with Italy in 1947, Del Ponte set out to train as a doctor but switched to law. I first interviewed her in another world, when Giovanni Falcone was making the inroads against Cosa Nostra in Sicily that would lead to him being blown up by the Mafia in 1992. Falcone was following the money trail through bank accounts in Switzerland, for which he needed help. His Swiss counterpart became Del Ponte. While meeting Falcone in Sicily, an attempt was made on both their lives; a bomb beneath his home was discovered by police. Now Del Ponte has a permanent armed bodyguard. She learnt to shoot but declines to carry a gun. After campaigning to get secretive Swiss banks reformed, she turned to crime-busting: tracking the accounts of dictators, drug cartels and arms smugglers as well as Cosa Nostra, all of which won her enemies, whose numbers increased when she took over at The Hague in 1999.

The violence that racked Croatia and Bosnia between 1991 and 1995, Kosovo four years later, and Rwanda in 1994 was impossible fully to record. Survivors of massacres, concentration camps and 'ethnic cleansing' refrain, in many cases, from discussing what happened.

But there is a detailed record of what occurred in Bosnia at least, as told from the blue witness chairs in The Hague's three courtrooms. Much of this story has been told to empty public and press galleries. 'It is not only about conviction of defendants,' said Del Ponte. 'At the end of all the trials, if we can say that we have established the facts of what happened, that will have been something.'

There have been remarkable moments - one woman who lost her menfolk at Srebrenica was given leave to address genocidal Krstic. She simply asked where she could find her son's remains; the defiance on the general's face cracked and he winced. Stakic's trial revealed life in the camps, with personalities like Dr Eso Satkovic from Prijedor, widely loved, who had been a UN medic. He had become a morale-booster for inmates amid the slaughter and was forever ministering to guards after brawls between them. But one burly witness was in tears recalling the night Satkovic was told 'this time, bring your stuff' and, knowing what this meant, bade farewell to cellmates and friends. 'I could not believe there was anyone in the world so evil as to kill Dr Eso,' said the witness.

'When you have a defendant like Krstic, and witnesses, we will have this kind of testimony,' says Del Ponte. 'But with Krajisnik we are dealing with a chain of command, so the hearings will not be the kind of thing journalists want to write about or show on TV.' The miasma of wiretaps and documents making up these cases, said one prosecutor, 'do not just appear out of nowhere. We have to look for them - very hard.'

The unfinished trial of Milosevic was seen by many as a farce, the former President turning the proceedings into a show. But Del Ponte remembers the 'feeling of great relief, above all, when he arrived - that the President was in custody after all that work we had done. I remember it well, it was a Thursday, no one was here - I was calling everyone, telling them to come in. And just to see him in court, after working day after day to get him there: it was the one thing the women of Srebrenica asked of me - to bring him in, and I said it will take time, but we must have him. I held a private meeting with him, in an empty courtroom, at a table - just Milosevic, me and the guards. He sat in front of me and was very angry. (Del Ponte laughs at the thought.) I presented myself - "I'm the prosecutor" - and told him that, as the accused, he had rights and offered him the possibility of an interview. And he started to make a political speech. I listened for a few minutes and said: "OK, I am now going to stop your speech." I said to the guards: "Take him away." And it gave me great satisfaction to see these two guards take him like that.'

The protection of Karadzic and Mladic by Serbia and the 'Serbian republic' half of Bosnia has been a theme of Del Ponte's tenure, with rumours of undermining by western capitals. Del Ponte has cajoled, hunted and shuttled between Serbia, Bosnia, the international forces and intelligence net, and the European Union, which she persuaded not to begin membership talks with Serbia until Karadzic and Mladic were in The Hague. The EU backtracked on that pledge.

'The international community was not willing to arrest them between 1995 and 1997, when it would have been so easy to do so,' fumes Del Ponte, 'all because of this Dayton agreement [which froze the war in December 1995] and worries about security. After that, they went into hiding.'

The government in Serbia, she says, has a policy of 'wanting not to arrest them, which they are able to do, but persuading them to voluntarily surrender. Mladic 'is the one they can deliver'. And 'when they tell me they cannot, I can either believe them and say "let's work together", or I cannot believe them'.

Del Ponte has one month, but The Hague has a long way to go before it is obliged to 'complete' in 2010. Her replacement is a Belgian, Serge Brammertz. Whether Karadzic and Mladic come in or not, the office Del Ponte hands over has prepared cases against crucial defendants, not least Momcilo Perisic, commander-in-chief of the Yugoslav army, and Milan Lukic, charged with overseeing house burnings when Muslim families were incinerated alive.

Del Ponte meets the accused when they arrive. 'I don't like to shake hands with them - I know what they have done.' Lukic 'was the perfect gentleman, well spoken. And when we had finished the meeting and stood up, he just took my hand and...He gave me un bacio alla mano [a kiss on the hand]. The devil,' she whispers. 'I said to my assistant, "I need to wash my hands".'

· This article was amended on December 16 2007. Carlo Del Ponte was quoted as saying 'un bacio al amno'. This should have read 'un bacio alla mano'. This has been corrected.